This invention relates to electronic compasses and to navigation systems including such compasses and more especially it relates to such compasses and navigation systems for use in vehicles.
The term vehicle when used herein is intended to include ships, boats and aircraft as well as land based vehicles such as cars, lorries or military vehicles and the term electronic compass as used herein defines a compass in which a bearing indication is afforded in dependence upon electronic signals provided by magnetic sensors responsive to the earths magnetic field.
Modern vehicles are constructed principally from steel or include significant steel parts having magnetic characteristics which distort the earth's magnetic field in and around the close proximity of the vehicle. Although electronic compasses per se are known, their use has hitherto been strictly limited in vehicles, since magnetic sensors essential to such compasses must either be placed on masts or extension arms in order to avoid spurious magnetic fields associated with the vehicle and the use of masts or the like is often not possible or at least undesirable or be subjected to an elaborate compensation process.
An important object of the present invention is to provide for a vehicle an electronic compass or a navigation system including such a compass, wherein spurious magnetic fields associated with the vehicle are compensated for, such that magnetic sensors forming a part of the compass may be accommodated within or close to the vehicle in which the compass is carried.